Help with ex husband

Let's start at beginning I was married to this man for 9 years we had a beautiful son who is 11 years old we got divorced due to him cheating on me we share our sons custody he has him summers and every other weekend during school year as its in our divorce decree..  well my son called me saying he doesn't want to come to the baby's birth I told him he had to and it's not a choice & this little kid had nerve to hang up on me twice!!!!! I will  be having a scheduled c section on Friday,  so I called again and his father answers the phone and I say did he just hang up on me and my ex laughs and he says our son doesn't want to go and if he doesn't want to go you can't force him.. I told him how is he going to miss on something so important in our sons life and he says that's not important for him it's important to you ( forgot to mention I remarried and this baby is current husbands baby) what would you ladies do in my situation?? Would you go get the kid anyway? Or do you just let it be and have him meet sister when summer is over and he has to come back???